Modern linear motion guide units are finding increased applications in diverse fields including various assembling machines, semiconductor manufacturing equipment, and so on. Corresponding to the downsizing requirement in the applied fields, the advanced sliding devices are more needed to meet miniaturization or downsizing in construction and maintenance-free working for lubrication. Especially, the micromechanical ball-splines frequently used as linear motion guide units in semiconductor manufacturing equipment, and so on, are challenged to meet the maintenance-free working for lubrication.
In a commonly-assigned U.S. Pat. No. 7,637,662B2, US counterpart of Japanese Laid-Open Patent Application No. 2006-38195A, there is described a rolling guide unit which allows greater freedom of design considerations, easier control of lubricant, and less resistance against sliding movement of the rolling elements. The prior rolling guide unit has a lubricant-impregnated member installed inside a cavity made in a cylindrical carriage of a slider, and a lubricant applicator built in an end cap of the slider to apply the lubricant around rolling elements while rolling through a turnaround passage in the end cap, the lubricant applicator being urged forcibly against the lubricant-impregnated member. With the prior rolling guide unit constructed as stated earlier, accordingly, the carriage is needed to have any extra space to provide the cavity for installation of the lubricant-impregnated member adjacent to the circulating circuit for the rolling elements. Further, the lubricant applicator has to have the desired size and stiffness enough to bear the squeeze against the lubricant-impregnated member. This means the prior rolling guide unit constructed as stated earlier is unsuited for the miniaturization or downsizing of the unit.
Another example of prior linear motion guide units is disclosed in a commonly-assigned U.S. Pat. No. 7,862,234B2, US counterpart of Japanese Laid-Open Patent Application No. 2008-82433A, in which the application points of lubricant around rolling elements are made in a turnaround passage to ensure proper and steady lubrication by the lubrication system that is simple in construction, with an accompanying sustainable maintenance-free condition for lubrication. A porous compact applicator impregnated with lubricant fits into a recess made to sink below an outward end surface of an end cap, which has a hole defined therein to communicate the recess with a turnaround passage. The porous compact applicator has a nose extending through the hole in the end cap to lead lubricant into the turnaround passage. The porous compact fits snugly into the recess in a fashion that the nose comes into rolling-touch at its tip with the rollers as they roll through the turnaround passage, applying the rollers with lubricant delivered from the nose. With the linear motion guide unit constructed as stated in this way, since the outward end surface of the end cap has a comparatively large area, the porous compact applicator to be laid on the substantially overall area of the outward end surface of the end cap has only stiffness enough allowing the porous compact applicator to fit easily into the recess in the end cap just by manual handling. Only installation of an end seal over the outward end surface of the end cap is necessary to make certain of steady application of lubricant around the rolling elements while rolling through the turnaround passage.
Though the prior linear motion guide unit constructed as stated in this way was befitting for maintenance-free operation for lubrication, yet it remained a major challenge to develop any miniature or micromechanical ball-spline. In conventional production of the miniature ball-spline in which tiny or minute parts were selected, discerned from each other and then assembled together, the assemblage of the tiny parts was found to be a formidable task. With the design considerations of adding the lubricating function to the end cap in the prior the ball-spline constructed as stated in this way, more especially, the parts and/or components for the end cap needed to be even smaller or tinier than in the prior miniature ball-spline. This meant there remained a major challenge about how to locate microscopic pieces or parts in place, then assemble them together, and join them together while keeping them in assembled relation into the finished end cap.
Following the ball-spline explained in the commonly-assigned U.S. Pat. No. 7,637,662 B2 as recited earlier, a ball-spline has been developed, which is improved to have lubricating function and more downsized to be applicable to a guide shaft having a diameter of from 2 to 6 mm. The subject matter disclosed herein is how to build a lubricant applicator in a miniature end cap with ease in assembling work and accuracy in location. The linear motion guide unit of the present invention, although following the miniature ball-spline with a built-in lubricating system developed earlier, is motivated to find a way out of deadlock or difficulty encountered in the conventional production process in which more downsized pieces or parts than ever are selected individually, discerned and then assembled together into the end cap. With the miniature ball-spline with built-in lubricating system of the present invention, in summary, a lubricant applicator of porous compact is built in an end cap and confined inside the end cap with a retainer plate which is kept in the end cap by means of a snap-fit engagement with the end cap to squeeze the lubricant applicator.